Canon Sx230hs Numbering Issue

For some reason every time I download photos to my computer the numbering starts over at 001. I have it set to number photos continuously regardless of ther memory card installed, but it doesn't do it. The first couple of weeks I had the camera it worked fine, but now the numbering has stopped working. I've changed nothing on the camera or my computer. I have verified the numbering setting in the camera set up is still on "Continuous."